The design and construction of non-wood bats has predominately been focussed on aluminum alloys and, to a lesser extent, composite materials such as graphite and glass fibers in an epoxy resin matrix. Historically, these conventional bats have been formed of a one-piece construction wherein the handle and the barrel are formed as a unitary (one-piece) structure, with the handle knob and barrel end cap being attached as separate structural components.
Performance of bats is primarily measured in terms of the speed at which the ball rebounds from the barrel. Over the years, bat manufacturers have made design changes to increase ball speed thus improving the performance of the bat. The principal way that ball speed has been increased is by thinning the wall in the barrel of the bat to increase the spring or trampoline effect when the ball impacts the barrel. An increase in ball speed could be obtained by modifying the barrel's circumferential flexibility due to the stiff transition between the barrel's tapered proximal end and the relatively thick-walled handle. As a result, design efforts to increase bat performance has focused on thinning the wall of the barrel to produce the desired spring effect noted previously.
The challenge to making one-piece thin wall aluminum bats is to have high performance and good durability. Persistent significant problems of barrel denting have occurred for high performance bats having relatively thin-walled barrels. Bat manufacturers have attempted to solve such problem by careful selection of aluminum alloys, but such attempts have not met with complete success.
Bats constructed of composite materials, such as graphite, fiberglass and/or aramid fiber-reinforced epoxy resins, have not met with much commercial success. In this regard, the designers of composite bats have followed the same design objectives to produce thin walled flexible barrel bats as described above. The impact strength of composite materials is much less than that for aluminum and aluminum alloys and thus it has been difficult to match the barrel flex of aluminum without breakage. As a result, composite material bats have been produced with a stiffer barrel which lacks the performance characteristics of the aluminum bats having flexible thin-walled barrels.
Recently, a two-piece bat construction has been proposed in U.S. Pat. No. 5,593,158 to Filice et al (the entire content of which is incorporated expressly by reference herein). According to this prior proposal, the handle and barrel are separate structural components having conforming taper segments with an elastomeric isolation union disposed therebetween. This elastomeric isolation union provides the only connection between the handle and the barrel and is said to reduce shock transmitted from the handle to the hands of a user when a ball is hit with the bat. The handle member on these types of bats is short in length and increases in diameter to facilitate connection to the larger diameter barrel member. This limited length and increase in diameter of the handle section minimizes the flexural response of the handle.